DESCRIPTION: Dr. Wanner describes a series of experiments designed to elucidate the role of three key proteins, PhoR, PhoB and PhoU (PstB), involved in inorganic phosphate signalling. PhoR and PhoB function together as a sensor-regulator pair and are members of the large family of two component regulatory systems. The sensor PhoR , which is an integral membrane protein, is thought to sense Pi levels outside the cytoplasmic membrane. Phosphate starvation stimulates PhoR to phosphorylate PhoB which then functions to turn on expression of many Pi starvation inducible (psi) genes, previously characterized by Dr. Wanner. Restoration of inorganic phosphate results in dephosphorylation of PhoB and deactivation of psi gene expression. PhoU and or PstB are thought to be essential for the deactivation process. Another feature of the system is inhibition at high phosphate levels which is thought to be due to sequestration of PhoB by a complex of proteins including PhoR, PhoU, PstB and proteins involved in high affinity phosphate transport. There are three specific aims in the proposal: (i) to determine the region(s) of PhoB that interact with PhoR and with PhoU (ii) to determine how PhoR kinase and phosphatase activities are regulated, what regions of PhoR interact with PhoB and PhoU and to identify the Pi signal domain in the protein (iii) to determine the role of PhoU and or PstB in deactivation of psi gene expression and to determine the regions of these proteins responsible for PhoB and PhoR recognition. Common to the three aims is the idea that PhoB, PhoR and PhoU interact.